Validation of immunodetection (ELISA) of ricin using a biological activity assay

The suitability of enzyme-linked immunosorbent assay (ELISA) for residual ricin toxicity determination was investigated in this study. Ricin was thermally treated at 80 to 90 °C for up to 9 min, and its residual concentration was determined by means of a commercial ELISA kit, and its bioactivity (amount of adenine released from DNA) was determined by means of a biological activity assay (BAA). Results showed that inactivation of ricin followed 1st-order kinetics. The half-life values for loss of bioactivity at 80, 85, and 90 °C were 1.93, 0.65, and 0.41 min, respectively. Similarly, the half-life values for reduction in ricin concentration determined by ELISA were 3.06, 0.79, and 0.43 min, respectively. The half-lives determined by both assays were only significantly different at 80 °C. The Z, Q(10), and Arrhenius activation energy values determined by both assays were dissimilar: 11.74 ˚C, 7.12 and 50.1 kcal/mol, respectively, by ELISA; and 14.87 °C, 4.71 and 39.5 kcal/mol, respectively, by BAA. Nevertheless, our findings indicate that the 2 assays were highly correlated (R(2) = 1), and it can be concluded that ELISA would be a reliable method for detecting residual toxicity of heat-treated ricin based on fraction lost. Practical Application: The results of this study indicate that immunodetection, even though not a direct measurement of the biological activity of ricin, is suitable for determining the residual bioactivity of ricin since immunodetection and the biological activity assay used in this investigation were highly correlated. Therefore, ELISA can be used for routine assessment of residual activity or toxicity of ricin in thermally treated foods.